For example, there are the Ni-MH secondary battery and the lead-acid secondary battery as batteries to be mounted as a power source for the electric motor-operated vehicle. The discharge capacity of such batteries gradually decreases through cyclic uses.
It is conceivable to carry out the maintenance including replacing, cleaning, and replenishing the electrolyte liquid of the battery after determining the deterioration of the battery by a voltage comparison method. However, the voltage comparison method requires cumbersome temperature compensation because the battery voltage itself changes with the ambient temperature.
Therefore, at the moment there is no simple, reliable means for constantly providing information on the necessity for the maintenance by accurately determining the state of deterioration of the battery as a power source of the electric motor-operated vehicle even during use, although such information is important.
The object of the invention made in view of the above situation is to provide method and device for monitoring deterioration in the storage battery that makes it possible to determine simply and reliably the state of deterioration in the storage battery capacity.